# How to Estimate How Much Clay You Need

Cluster: Using Claybook
URL: https://claybook.studio/blog/how-to-estimate-clay-weight/

# How to Estimate How Much Clay You Need

Guessing grams is how you get heavy mugs and short bowls. Claybook’s clay weight estimator turns a target size into a starting weight, using the clay body’s density and shrinkage.

There is a free web version at the [clay weight estimator](/guides/clay-weight-estimator.html). The in-app tool is the same idea, wired to the clays and shapes in your library.

If you want a cheat sheet of starting weights first, use the [Ultimate Clay Weight Guide](/blog/ultimate-clay-weight-guide/). The estimator is for when you have actual dimensions.

## What the estimator is calculating

It estimates the clay volume of the form (walls, floor, optional foot), then converts volume to grams with wet density, and scales for shrinkage so the fired piece lands near the size you typed.

You are not getting a kiln-certified number. You are getting a better first ball than “this feels like a mug.”

## Step-by-step in Claybook

1. Open **Tools**
2. Tap **Clay weight estimator**
3. Pick a shape: mug, bowl, cylinder, vase, plate, or a custom shape you added
4. Enter the dimensions the shape asks for (height, width, wall thickness, and so on)
5. Choose the clay from your library, or Custom with density and shrinkage
6. Read the suggested weight range
7. Optional: turn on foot trimming if you will cut a foot ring, and enter outer diameter, inner diameter, and trim depth

Weigh that ball. Throw. Log the real starting weight on the craft. Next time you will trust your own result more than the estimate.

## Use your clay, not a generic stoneware

Density and shrinkage change the answer. Porcelain is not the same as groggy sculpture clay at the same finished size.

Add the bag in **Clays** with:

* Wet density (often near 1.8 g/cm³ if the bag is silent)
* Shrinkage percent

Then pick that clay in the estimator. Setup: [How to Add a Clay Body in Claybook](/blog/how-to-add-a-clay-body/).

If the fired piece missed the size, fix shrinkage first with [How to Calculate Clay Shrinkage in Claybook](/blog/how-to-calculate-clay-shrinkage/), then re-run the estimate.

## Foot trim is extra clay, not leftover luck

If you throw extra for a foot ring, the estimator can add that volume.

Turn on the foot trim option and enter:

* Foot outer diameter
* Foot inner diameter (the well)
* Trim depth

Skip this for pieces you will leave with a simple cut-off foot. Include it for bowls and mugs you always trim.

## Custom shapes

The Shapes tab holds forms the estimator can use. If you repeat a studio-specific form (lidded jar, oval baker), add a custom shape with the measurements you actually take.

Then the estimator is speaking your language, not a generic cylinder.

## After you throw, close the loop

The estimate is a plan. The craft record is the truth.

On the piece, add a **Formed** step with the grams you actually used. If the form collapsed or felt thin, note it. Next session, nudge the estimate or your wall thickness instead of starting from zero.

That habit is the whole point of [The Case for Weighing Your Clay](/learn/the-case-for-weighing-your-clay/).

## When a chart is faster than the calculator

Use a chart for ballpark work:

* Small bowl often starts near 300 g
* Everyday mug often starts near 350 to 450 g
* See [How Much Clay Do You Need for a Mug?](/blog/how-much-clay-for-a-mug/)

Use the estimator when a customer gave you centimeters, when a lid has to fit, or when you changed clay bodies.

## Common mistakes

* Entering fired size but using a clay with 0% shrinkage
* Ignoring wall thickness, then wondering why the weight feels light
* Estimating in cm, throwing to a rib marked in inches
* Never logging the real weight, so the estimator never gets calibrated by your hands

## Takeaway

Pick the shape, type the size you want, pick the clay you will actually wedge. Weigh the suggested ball. Save that number on the project. Estimates get you on the wheel faster. Logged weights make the next set match.